Advances in cell-replacement therapy for Type I diabetes mellitus and a shortage of transplantable islets of Langerhans have focused interest on developing sources of insulin-producing cells, or β cells, appropriate for engraftment. One approach is the generation of functional β cells from pluripotent stem cells, such as, for example, embryonic stem cells.
In vertebrate embryonic development, a pluripotent cell gives rise to a group of cells comprising three germ layers (ectoderm, mesoderm, and endoderm) in a process known as gastrulation. Tissues such as, for example, thyroid, thymus, pancreas, gut, and liver, will develop from the endoderm, via an intermediate stage. The intermediate stage in this process is the formation of definitive endoderm. Definitive endoderm cells express a number of markers, such as, HNF-3 beta, GATA-4, Mixl1, CXCR4 and SOX-17.
Formation of the pancreas arises from the differentiation of definitive endoderm into pancreatic endoderm. Cells of the pancreatic endoderm express the pancreatic-duodenal homeobox gene, PDX-1. In the absence of PDX-1, the pancreas fails to develop beyond the formation of ventral and dorsal buds. Thus, PDX-1 expression marks a critical step in pancreatic organogenesis. The mature pancreas contains, among other cell types, exocrine tissue and endocrine tissue. Exocrine and endocrine tissues arise from the differentiation of pancreatic endoderm.
Cells bearing the features of islet cells have reportedly been derived from embryonic cells of the mouse. For example, Lumelsky et al. (Science 292:1389, 2001) report differentiation of mouse embryonic stem cells to insulin-secreting structures similar to pancreatic islets. Soria et al. (Diabetes 49:157, 2000) report that insulin-secreting cells derived from mouse embryonic stem cells normalize glycemia in streptozotocin-induced diabetic mice.
In one example, Hori et al. (PNAS 99: 16105, 2002) disclose that treatment of mouse embryonic stem cells with inhibitors of phosphoinositide 3-kinase (LY294002) produced cells that resembled β cells.
In another example, Blyszczuk et al. (PNAS 100:998, 2003) reports the generation of insulin-producing cells from mouse embryonic stem cells constitutively expressing Pax4.
Micallef et al. reports that retinoic acid can regulate the commitment of embryonic stem cells to form PDX-1 positive pancreatic endoderm. Retinoic acid is most effective at inducing PDX-1 expression when added to cultures at day 4 of embryonic stem cell differentiation during a period corresponding to the end of gastrulation in the embryo (Diabetes 54:301, 2005).
Miyazaki et al. reports a mouse embryonic stem cell line over-expressing PDX-1. Their results show that exogenous PDX-1 expression clearly enhanced the expression of insulin, somatostatin, glucokinase, neurogenin3, P48, Pax6, and HNF6 genes in the resulting differentiated cells (Diabetes 53: 1030, 2004).
Skoudy et al. reports that activin-A (a member of the TGFβ superfamily) upregulates the expression of exocrine pancreatic genes (p48 and amylase) and endocrine genes (PDX-1, insulin, and glucagon) in mouse embryonic stem cells. The maximal effect was observed using 1 nM activin-A. They also observed that the expression level of insulin and PDX-1 mRNA was not affected by retinoic acid; however, 3 nM FGF-7 treatment resulted in an increased level of the transcript for PDX-1 (Biochem. J. 379: 749, 2004).
Shiraki et al. studied the effects of growth factors that specifically enhance differentiation of embryonic stem cells into PDX-1 positive cells. They observed that TGFβ2 reproducibly yielded a higher proportion of PDX-1 positive cells (Genes Cells. 2005 June; 10(6): 503-16.).
Gordon et al. demonstrated the induction of brachyury+/HNF-3 beta+endoderm cells from mouse embryonic stem cells in the absence of serum and in the presence of activin along with an inhibitor of Wnt signaling (US2006/0003446A 1).
Gordon et al. (PNAS, Vol 103, page 16806, 2006) states “Wnt and TGF-beta/nodal/activin signaling simultaneously were required for the generation of the anterior primitive streak”.
However, the mouse model of embryonic stem cell development may not exactly mimic the developmental program in higher mammals, such as, for example, humans.
Thomson et al. isolated embryonic stem cells from human blastocysts (Science 282:114, 1998). Concurrently, Gearhart and coworkers derived human embryonic germ (hEG) cell lines from fetal gonadal tissue (Shamblott et al., Proc. Natl. Acad. Sci. USA 95:13726, 1998). Unlike mouse embryonic stem cells, which can be prevented from differentiating simply by culturing with Leukemia Inhibitory Factor (LIF), human embryonic stem cells must be maintained under very special conditions (U.S. Pat. No. 6,200,806; WO 99/20741; WO 01/51616).
D'Amour et al. describes the production of enriched cultures of human embryonic stem cell-derived definitive endoderm in the presence of a high concentration of activin and low serum (D'Amour K A et al. 2005). Transplanting these cells under the kidney capsule of mice resulted in differentiation into more mature cells with characteristics of some endodermal organs. Human embryonic stem cell-derived definitive endoderm cells can be further differentiated into PDX-1 positive cells after addition of FGF-10 (US 2005/0266554A1).
D'Amour et al. (Nature Biotechnology—24, 1392-1401 (2006)) states “We have developed a differentiation process that converts human embryonic stem (hES) cells to endocrine cells capable of synthesizing the pancreatic hormones insulin, glucagon, somatostatin, pancreatic polypeptide and ghrelin. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm, gut-tube endoderm, pancreatic endoderm and endocrine precursor en route to cells that express endocrine hormones”.
In another example, Fisk et al. reports a system for producing pancreatic islet cells from human embryonic stem cells (US2006/0040387A1). In this case, the differentiation pathway was divided into three stages. Human embryonic stem cells were first differentiated to endoderm using a combination of n-butyrate and activin-A. The cells were then cultured with TGFβ antagonists such as Noggin in combination with EGF or betacellulin to generate PDX-1 positive cells. The terminal differentiation was induced by nicotinamide.
In one example, Benvenistry et al. states: “We conclude that over-expression of PDX-1 enhanced expression of pancreatic enriched genes, induction of insulin expression may require additional signals that are only present in vivo” (Benvenistry et al., Stem Cells 2006; 24:1923-1930).
Current methods to culture human embryonic stem cells requires the use of either extracellular matrix proteins or a fibroblast feeder layer, or the addition of exogenous growth factors, such as, for example, bFGF.
In one example, Cheon et al (BioReprod DOI: 10.1095/biolreprod.105.046870, Oct. 19, 2005) disclose a feeder-free, serum-free culture system in which embryonic stem cells are maintained in unconditioned serum replacement (SR) medium supplemented with different growth factors capable of triggering embryonic stem cell self-renewal.
In another example, Levenstein et al (Stem Cells 24: 568-574, 2006) disclose methods for the long-term culture of human embryonic stem cells in the absence of fibroblasts or conditioned medium, using media supplemented with bFGF.
In another example, US20050148070 discloses a method of culturing human embryonic stem cells in defined media without serum and without fibroblast feeder cells, the method comprising: culturing the stem cells in a culture medium containing albumin, amino acids, vitamins, minerals, at least one transferrin or transferrin substitute, at least one insulin or insulin substitute, the culture medium essentially free of mammalian fetal serum and containing at least about 100 ng/ml of a fibroblast growth factor capable of activating a fibroblast growth factor signaling receptor, wherein the growth factor is supplied from a source other than just a fibroblast feeder layer, the medium supported the proliferation of stem cells in an undifferentiated state without feeder cells or conditioned medium.
In another example, US20050233446 discloses a defined media useful in culturing stem cells, including undifferentiated primate primordial stem cells. In solution, the media is substantially isotonic as compared to the stem cells being cultured. In a given culture, the particular medium comprises a base medium and an amount of each of bFGF, insulin, and ascorbic acid necessary to support substantially undifferentiated growth of the primordial stem cells.
In another example, U.S. Pat. No. 6,800,480 states “In one embodiment, a cell culture medium for growing primate-derived primordial stem cells in a substantially undifferentiated state is provided which includes a low osmotic pressure, low endotoxin basic medium that is effective to support the growth of primate-derived primordial stem cells. The basic medium is combined with a nutrient serum effective to support the growth of primate-derived primordial stem cells and a substrate selected from the group consisting of feeder cells and an extracellular matrix component derived from feeder cells. The medium further includes nonessential amino acids, an anti-oxidant, and a first growth factor selected from the group consisting of nucleosides and a pyruvate salt.”
In another example, US20050244962 states: “In one aspect the invention provides a method of culturing primate embryonic stem cells. One cultures the stem cells in a culture essentially free of mammalian fetal serum (preferably also essentially free of any animal serum) and in the presence of fibroblast growth factor that is supplied from a source other than just a fibroblast feeder layer. In a preferred form, the fibroblast feeder layer, previously required to sustain a stem cell culture, is rendered unnecessary by the addition of sufficient fibroblast growth factor.”
In a further example, WO2005065354 discloses a defined, isotonic culture medium that is essentially feeder-free and serum-free, comprising: a. a basal medium; b. an amount of bFGF sufficient to support growth of substantially undifferentiated mammalian stem cells; c. an amount of insulin sufficient to support growth of substantially undifferentiated mammalian stem cells; and d. an amount of ascorbic acid sufficient to support growth of substantially undifferentiated mammalian stem cells.
In another example, WO2005086845 discloses a method for maintenance of an undifferentiated stem cell, said method comprising exposing a stem cell to a member of the transforming growth factor-beta (TGFβ) family of proteins, a member of the fibroblast growth factor (FGF) family of proteins, or nicotinamide (NIC) in an amount sufficient to maintain the cell in an undifferentiated state for a sufficient amount of time to achieve a desired result.
Additionally, formation of pancreatic endocrine cells, pancreatic hormone expressing cells, or pancreatic hormone secreting cells from human embryonic cells may require genetic manipulation of the human embryonic stem cells. Transfection of human embryonic stem cells using traditional techniques, such as, for example, lipofectamine or electroporation is inefficient.
WO2007027157 discloses a method comprising: (a) providing an embryonic stem (ES) cell; and (b) establishing a progenitor cell line from the embryonic stem cell; in which the progenitor cell line is selected based on its ability to self-renew. Preferably, the method selects against somatic cells based on their inability to self renew. Preferably, the progenitor cell line is derived or established in the absence of co-culture, preferably in the absence of feeder cells, which preferably selects against embryonic stem cells. Optionally, the method comprises (d) deriving a differentiated cell from the progenitor cell line.
Therefore, there still remains a significant need to develop conditions for establishing pluripotent stem cell lines that can be expanded to address the current clinical needs, while retaining the potential to differentiate into pancreatic endocrine cells, pancreatic hormone expressing cells, or pancreatic hormone secreting cells.